The length of a thrust reverser's door is one of the design parameters which is important, as it plays a direct role in the thrust reverser's effectiveness and efficiency. The deployed doors deflect air to create a drag force for slowing down the aircraft, and the size of the deployed door therefore tends to affect the amount of drag generated (i.e. braking performance).
However, a trade-off exists, as larger doors tend to be heavier and introduce more losses when stowed, and so it is generally required to optimize door length to obtain acceptable performance and efficiency.
It is therefore desirable to, among other things, have a thrust reverser door which provides improved performance while decreasing losses.